Publikace

We report the photosensitization of crystalline silicon via energy transfer using covalently attached protoporphyrin IX (PpIX) derivative molecules at different distances via changing the diol linker to the surface. The diol linker molecule chain length was varied from 2 carbon to 10 carbon lengths in order to change the distance of PpIX to the Si(111) surface between 6 A and 18 A. Fluorescence quenching as a function of the PpIX-Si surface distance showed a decrease in the fluorescence lifetime by almost two orders of magnitude at the closest separation. The experimental fluorescence lifetimes are explained theoretically by a classical Chance-Prock-Silbey model. At a separation below 2 nm, we observe for the first time, a Forster like dipole-dipole energy transfer with a characteristic distance of R-o = 2.7 nm.

The concept of light scattering and light trapping used to be inevitable for maintaining the technology of amorphous silicon profitable for long time. This strong light trapping concept will again rise in importance for current technologies, but fast methods of simulations will have priority in more comprehensive optimization over the time-consuming methods such as finite element or FDTD method. In this paper we present a novel approach of optical simulation of multilayer with accounting surface scattering that is based on complex transfer matrix concept, similarly as the non-scattered Fresnel component. This allows treatment of light trapping and effects of evanescent waves also for the scattered light. The only condition is to include phase randomization present in the case of light scattering.

Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5–6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4–6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 1013 cm–2), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiOx substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

Well-defined covalent surface functionalization of diamond is a crucial, yet nontrivial, matter because of diamond's intrinsic chemical inertness and stability. Herein, we demonstrate a two-step functionalization approach for H-terminated boron doped diamond thin films, which can lead to significant advances in the field of diamond hybrid photovoltaics. Primary diamond surface functionalization is performed via electrochemical diazonium grafting of in situ diazotized 4-iodoaniline. The freshly grafted iodophenyl functional moieties are then employed to couple a layer of thiophene molecules to the diamond surface via two well-established Pd-catalyzed cross-coupling reactions, i.e., Stile and Sonogashira. X-ray photoelectron spectroscopy analysis indicates a dense coverage and successful cross-coupling in both cases. However, we find that the Stille reaction is generally accompanied by severe surface contamination, in spite of process optimization and thorough rinsing. Sonogashira cross-coupling on the other hand provides a clean, high quality functionalization over a broad range of reaction conditions. The protocols employing Sonogashira reactions thus appear to be the method of choice toward future fabrication of high-performance dye-functionalized diamond electrodes for photovoltaic applications.

Surface modification of detonation nanodiamonds (DNDs) is a key factor for their application in diverse fields of science and technology. In this work we report on an easy and low-cost method for modifying water-dispersed DNDs by atmospheric DC plasma afterglow. DNDs were used in either as-received form (asrec-DND) or were oxidized by air-annealing at 450 °C for 30 minutes (O-DND). The influence of applied voltage and thus the type of discharge (corona discharge at 10 kV or transient spark discharge at 15 kV) and treatment duration (5 and 10 minutes) on the surface chemistry of DNDs was evaluated by Fourier Transform Infrared (FTIR) spectroscopy supported by X-ray photoelectron spectroscopy (XPS) and dynamic light scattering (DLS). Treated asrec-DNDs revealed stable positive ζ-potential (30 mV) during rearrangement of oxygen-containing moieties (changes in area below 1250 cm−1) as well as CHx groups, reflected in the enormous enhancement of the band at 1328 cm−1 and disappearance of the C[double bond, length as m-dash]C band at 1589 cm−1. On the other hand, the DC discharge afterglow had only minor impact on the surface chemistry of O-DND particles, as detected by FTIR and XPS, while a negative change of ζ-potential by up to 22 mV occurred. O-DND particles dried in vacuum also exhibited a noticeable catalytic effect towards hydrocarbons.

Optical absorptance spectroscopy of polycrystalline CH3NH3PbI3 films usually indicates the presence of a PbI2 phase, either as a preparation residue or due to film degradation, but gives no insight on how this may affect electrical properties. Here, we apply photocurrent spectroscopy to both perovskite solar cells and coplanar-contacted layers at various stages of degradation. In both cases, we find that the presence of a PbI2 phase restricts charge-carrier transport, suggesting that PbI2 encapsulates CH3NH3PbI3 grains. We also find that PbI2 injects holes into the CH3NH3PbI3 grains, increasing the apparent photosensitivity of PbI2.

There exist many method used for photovoltaic (PV) modules and systems diagnostics. One of the less conventional is impedance analysis of PV cells or modules which gives additional information about measured cell, module respectively. Due to high amount of possible sources of uncertainties and low repeatability when performed under samples irradiation, the evaluation of obtained results is relatively complicated. In this paper, the comparison of conventional methods and impedance analysis and its possible evaluation and limits are presented.

Purpose – The purpose of this paper is to increase the reliability of manufactured electronics and to reveal reliability significant factors. The experiments were focused especially on the influence of the reflow oven parameters presented by a heating factor. Design/methodology/approach – The shear strength of the surface mount device (SMD) resistors and their joint resistance were analyzed. The resistors were assembled with two Sn/Ag/Cu-based and one Bi-based solder pastes, and the analysis was done for several values of the heating factor and before and after isothermal aging. The measurement of thickness of intermetallic compounds was conducted on the micro-sections of the solder joints. Findings – The shear strength of solder joints based on the Sn/Ag/Cu-based solder alloy started to decline after the heating factor reached the value of 500 s · K, whereas the shear strength of the solder alloy based on the Bi alloy (in the measured range) always increased with an increase in the heating factor. Also, the Bi-based solder joints showed shear strength increase after isothermal aging in contrast to Sn/Ag/Cu-based solder joints, which showed shear strength decrease. Originality/value – The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between reliability and other technological parameters such as solder alloy type, surface finish and parameters of the soldering process.